Constitutients of Rice Straw Smoke-81



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Project Leader and Principal UC Investigators

D.P.H. Hsieh and J.N. Seiber, Department of Environmental Toxicology, UC Davis


Objectives of this project are to: 1) develop analytical methods for separating rice straw smoke extract, a very complex mixture, into several fractions of simpler chemical composition; 2) determine which classes of compounds are responsible for mutagenic activity in the Ames Salmonella Mutagenicity Assay; and 3) identify specific compounds within each fraction.

The Ames Assay helps predict the potential human health hazard of specific chemicals or mixture of chemicals. Each sample of smoke collected for assay came from 20 pounds of burned rice straw. The smoke was collected on air filters and extracted. The smoke extract was separated into several fractions of simpler chemical composition. The whole smoke extract and the fractions were then tested for their capacity to cause mutagenic activity in the Ames Assay relative to the mutagenic activity of a standard, benzo(a)pyrene. Benzo(a)pyrene, a compound present in diesel exhaust, coal tar and other combustion products, is known to cause a high level of mutagenicity in the Ames Assay.

The whole rice straw smoke extract was weakly mutagenic in the Ames Assay. The activity of the whole extract was 1.5 percent of the activity of benzo(a)pyrene, while fractions IV, V, VI, and VII were 5.4 percent, 7 percent, 7 percent, and 11 percent, respectively. Chemical analysis indicated the presence of oxidized aromatic hydrocarbons in fraction IV and the presence of nitrogen heterocycles and amines in fractions V and VI. These types of compounds have also been found in smoke from other sources, such as wood stoves, open leaf burning and diesel exhaust.

As the content of rice straw smoke may change while exposed to atmospheric conditions such as sunlight and oxidants, the study of smoke downwind from a burned field is particularly relevant, especially as the population centers are, for the most part, downwind from the fields which are burned. It would also be of interest to make a comparison between rice straw smoke and smoke from other agricultural byproducts subject to burning as well as to air in urban centers. The methods developed so far are essential to such comparisons.


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